June 2015 – JAPAN – The main reason why the earthquake that occurred west of the Ogasawara Islands on Saturday night shook most parts of the country — in addition to the temblor’s strength — was that the quake’s focus was extremely deep, according to seismologists and the Japan Meteorological Agency. The shaking was remarkably strong in the Kanto region. Seismologists attribute this to fact that the seismic waves reached the region after passing through undersea tectonic plates, which are harder than land plates and transmit waves more easily. The agency said strong seismic waves can reach faraway places in such a “region of abnormal seismic intensity.” Prof. Takashi Furumura of the University of Tokyo’s Earthquake Research Institute said that tectonic plates lie on top of one another in a complicated way under the Japanese archipelago and under the surrounding seas.

The Pacific Plate is the deepest and descends mainly below the Philippine Sea Plate, reaching deep under the Japanese archipelago. Yuichiro Tanioka, a professor of seismology at Hokkaido University, said: “Undersea plates are harder than land plates. Thus, seismic waves running through the plates [under the sea] tend not to weaken.” It is believed that the seismic waves that reached the Kanto region initially ran along the Pacific Plate, headed for shallower offshore areas, and then spread to another plate contacting the Pacific Plate. This is probably why, seismologists said, the waves did not weaken remarkably.

In September 2013, a magnitude-6.8 earthquake occurred about 450 kilometers deep off Torishima island of Tokyo. The quake produced shaking of up to 4 on the Japanese seismic intensity scale of 7 in wide areas from Hokkaido to the Kanto region. A magnitude-6.7 earthquake occurred about 370 kilometers deep off Kyoto Prefecture in July 2007, shaking a wide range of places. Hokkaido, far from the epicenter, recorded shaking of up to 4 on the Japanese seismic intensity scale. –Japan News

9 Responses to The depth of 7.8 magnitude Japanese earthquake caused widespread shaking

Just an observation from reviewing the posted picture. If quakes or some quakes occur at such a deep level within the earth, does that undermine the stability of the land mass above it?
For example, removing the dirt from under the foundation of a house?
Am I thinking too much here?

Doesn’t undermine the stability of the land mass under it, but it does agitate the land along the plate boundaries in subduction zones – the west coast of the US and Chile are cases in point. Here is where you have your greatest concentration of earthquakes and volcanic mountain ranges.

On the usgs site today, two fairly significant sized shallow depth quakes were recorded off the coast of Oregon (5.5 & 5.8, at 15k & 10k), yet hardly anything showed on the shake map, and nor were these events shown in bold red type! Wondered why the downplay?

http://www.ibtimes.com/fracking-resumes-denton-texas-after-governor-outlaws-local-bans-oil-gas-drilling-1947031
“Natural gas drilling is starting up again in Denton, Texas, despite the city’s 7-month-old ban on hydraulic fracturing. Vantage Energy resumed operations Monday at its Denton well just weeks after Gov. Greg Abbott passed a law prohibiting cities from banning fracking on their home turf. Three activists were arrested at the drill site Monday morning after attempting to block an access road.
“The Texas ban is part of a broader movement in oil- and gas-rich states to restrict decisions about fracking, drilling, wastewater disposal and pipelines to state regulators and commissioners — leaving municipalities, local agencies and citizens with limited control over energy activities.
“In Ohio, the state Supreme Court ruled in February that the state has “exclusive authority” and that cities can neither ban nor regulate fracking. On Saturday, Oklahoma Gov. Mary Fallin signed a bill that similarly prohibits cities from enacting drilling bans, despite local concerns over the rising number of earthquakes tied to fracking activity in the state. …”

When “state regulators and commissioners”, acting on behalf of “corporate interests” (be they “businesses” or systems of “taxation” [centralized governments] that profit from business profit), have more “power” than the citizenry . . . we have fascism.

here’s another:http://ecowatch.com/2015/03/15/jon-stewart-gov-christie-exxon-settlement/
““Did Satan’s skunk get diarrhea?,” Jon Stewart said last week in reference to (the Exxon settlement)…
“According to Workers World, “The oil giant and its predecessor companies have been polluting New Jersey’s wetlands for over a century. It was held liable for poisoning 1,500 acres around the Bayway refinery in Linden and facilities in Bayonne. Linden became a cancer cluster for New Jersey refinery workers.”
“Now, it’s being reported that New Jersey Gov. Chris Christie interfered with the state’s $9 billion lawsuit against Exxon, making the final settlement a mere $250 million.”